1. Field of the Invention
The present invention relates to a semiconductor device having a so-called SOI (Semiconductor On Insulator) structure in which a semiconductor layer is formed on a substrate via an insulating film, and a manufacturing method thereof.
2. Description of the Related Art
Conventionally, semiconductor devices, whose semi-conductive region has a thickness of several hundred μm, have the superficial several μm thickness function as the device, and the remaining several hundred μm semi-conductive region is used as a support substrate. However, when the surface of the semi-conductive region of such a semiconductor device is made to function as the device, an electric current also flows into the region used as the support substrate, making electric charges to pool therein. The pool of electric charges in the support substrate is a disturbance against improving the switching speed of the semiconductor device and reducing electricity consumption.
Hence, as disclosed in, for example, Unexamined Japanese Patent Application KOKAI Publication No. H6-120458, such a semiconductor device is developed, which has a Semiconductor On Insulator structure (hereinafter referred to as SOI structure), which has an insulating layer between the portion used as the device and the portion used as the substrate so as not to allow the electric charges to pool in the support substrate.
An example of the formation of a conventional diode having the SOI structure is shown in FIG. 8. As shown in FIG. 8, a semiconductor device 80 comprises a P type semiconductor substrate 81, an insulating film 82, an N− type semiconductor region 83, an N+ type semiconductor region 84, a P+ type semiconductor region 85, an anode electrode 87, and a cathode electrode 88. As a method for increasing the voltage withstand characteristic of the semiconductor device 80, a method of increasing the thickness of the insulating film 82 has conventionally been employed.